Interference in a pair of gears is avoided, if the addendum circles of both the gears intersect common tangent to the base circles with in the points of tangency.

Match the following:
List-$${\rm I}$$
(A) Worm gears
(B) Cross helical gears
(C) Bevel gears
(D) Spur gears

List-$${\rm I}{\rm I}$$
1. Parallel shafts
2. Non-parallel, intersecting shafts
3. Non-parallel, non-intersecting shafts
4. Large speed ratios

Machine tool, structures are made ................. for high process capability (tough/ rigid/ strong)